Ethylene polymers such as polyethylene homopolymers and ethylene-propylene copolymers may be produced under various polymerization conditions and employing various polymerization catalysts. Such polymerization catalysts include Ziegler-Natta catalysts and non-Ziegler-Natta catalysts, such as metallocenes and other transition metal catalysts which are typically employed in conjunction with one or more co-catalysts. The polymerization catalysts may be supported or unsupported.
Ethylene homopolymers or copolymers may be produced under various conditions in polymerization reactors which may be batch type reactors or continuous reactors. Continuous polymerization reactors typically take the form of loop-type reactors in which the monomer stream is continuously introduced and a polymer product is continuously withdrawn. For example, the production of polymers such as polyethylene or ethylene-propylene copolymers involve the introduction of the monomer stream into the continuous loop-type reactor along with an appropriate catalyst system to produce the desired ethylene homopolymer or copolymer. The resulting polymer is withdrawn from the loop-type reactor in the form of a “fluff” which is then processed to produce the polymer as a raw material in particulate form as pellets or granules. It is often the practice in the production of ethylene homopolymers and ethylene C3+ alpha olefin copolymers to employ substantial amounts of molecular weight regulators such as hydrogen to arrive at polymers or copolymers of the desired molecular weight. Typically in the polymerization of ethylene, hydrogen may be employed as a regulator with the hydrogen being introduced into the monomer feed stream in amounts of about 10 mole % and higher of the ethylene feed stream.